The American Petroleum Institute guideline provides a methodology for calculating the risks of equipments installed in refineries or petrochemical plants. However, especially in connection with consequence analysis, there are limitations of its direct application to petrochemical plant. As a principal cause, only representative material is recommended for the risk evaluation while the equipment contains numerous materials. The objectives of this paper are to propose an enhanced risk-based inspection (RBI) method to resolve above shortcomings and to assess the risks of typical petrochemical equipments. In this respect, a RBI program including a material management database is developed to fully incorporate the characteristics of different materials. The proposed program consists of qualitative, semi-quantitative, and quantitative evaluation modules in which representative material, as well as toxic materials, is selected automatically for comparison to those getting from the current guideline. It has been applied to assess the risks of major equipments in ethylene facility such as vessel and column. Thereby, realistic evaluation results were obtained and applicability of the proposed RBI program was proven.
ABSTRACT Heat exchangers comprise thousands of tubes having U‐shaped portions. Rotating bending method has been widely utilized to make U‐bends. Although this method shows an excellent performance, cracks have been frequently detected in the U‐bends due to residual stresses induced by bending. In this paper, the bending process is simulated based on elastic–plastic finite element analyses in order to investigate the magnitude and distribution of the residual stresses including the effects of operating pressure. Analyses results show that the residual stress increases as the radius of U‐bend decreases and that operating pressure has a detrimental effect in terms of stress corrosion cracking at the intrados of U‐bend. It is thought that these results can be utilized for the estimations of fracture mechanics parameters such as limit load, stress intensity factor and J‐integral, prevention of the cracking, and establishment of the optimum inspection strategy for the heat exchanger tubes.
The design of major industrial facilities for the prevention of fatigue failure is customarily done by defining a set of transients and performing a calculation of cumulative usage factor. However, sometimes, the inherent conservatism or lack of details as well as unanticipated transients in old plant may cause maintenance problems. Even though several famous on-line monitoring and diagnosis systems have been developed world-widely, in this paper, a new system for fatigue monitoring and life evaluation of crane is proposed to reduce customizing effort and purchasing cost. With regard to the system, at first, comprehensive operating transient data has been acquired at critical locations of crane. The real-time data were classified, by using adaptive resonance theory that is one of typical artificial neural network, into representative stress groups. Then the each classified stress pattern was mapped to calculated cumulative usage factor in accordance with ASME procedure. Thereby, promising results were obtained for the crane and it is believed that the developed system can be applicable to other major facilities extensively.
During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.
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